Instant water heater with PTC plastic conductive electrodes

ABSTRACT

An instant water heater utilizing positive temperature coefficient plastic electrically conductive material structures for electrodes. The heating of the water is not generated by the electrodes, but instead by the resistance of the water to the electrical current flowing between them. The material of the electrodes undergoes a phase change at certain temperatures when whereby it converts from electrically conductive to electrically non-conductive at a predetermined temperature. The output temperature of the water is determined by a combination of the area of the electrodes that confront one another, the water&#39;s conductivity, the flow rate of the water and the current limiting capability of the conductive electrode materials positive temperature coefficient, which reduces or stops the heating of the water when the intended water temperature is achieved.

CROSS REFERENCE TO OTHER APPLICATIONS

This is a continuation-in-part of applicant's co-pending U.S.application Ser. No. 11/111,670, filed Apr. 21, 2005, which is not beingabandoned.

FIELD OF THE INVENTION

An instant water heater which heats water flowing between two immersedelectrodes, using improved electrodes with positive temperature cutoff(PTC) properties, increased efficiency and longevity.

BACKGROUND OF THE INVENTION

This invention relates to water heaters of the type which heats waterthat flows between two electrodes, rather than by providing a hotelement which is contacted by the water. In this invention, the water isheated by electrical current flowing through the water when the water isbetween the two electrodes.

So-called “instant” water heaters differ from conventional water heatersby their lack of a storage tank for hot water. Instead of heating andstoring water for future usage, instant water heaters accept cold orcool water, heat it, and deliver it directly to the user point ondemand. Such heaters find their most common usage in sink faucets,showers and tubs, although they can be provided for any other usage thatrequires hot water.

Among their advantages is that they can be placed very near to the usepoint. Pipes of substantial length need not be emptied of cold waterbefore hot water arrives from a central source, for example. Also, it ismuch easier to run an electrical circuit to a distant heater than toprovide a distant tank, and a long pipe to convey hot water from acentral source to a distant use point.

Legionnaire's Disease is well known as a consequence of water stored forlong periods at moderate temperature. Having no storage of the water atall profoundly reduces risk of such disease.

Presently-known instant water heaters do have major disadvantages,including short product life, dry-fire burn-out, short service life,liability to water damage, moderate rates of flow, high energyconsumption, and release of metal ions into the water.

Another disadvantage of existing instant water heaters is theirinability to accommodate varying input voltages and amperage along withwater flow that matches their intended use. A complaint often heard isthat the wrong instant water heater was purchased from many differentavailable models. The necessary wide range of variables, such asvoltage, circuit breaker amperage, and service flow in gallons is simplytoo confusing for many customers.

It is yet another disadvantage of existing instant water heaters thatthey often burn out or break coils due to water hammering, air in thewater lines, or current overloads. These pose an electrical danger fromdirect contact of live broken coil ends to the water. The electricalcurrent then passes directly into the water. Manifolds that areconnected to ground with a grounding wire corrode, and it is only amatter of time before a corroded manifold or a burned out coil releasesa full current into the water and out a faucet or other plumbing fixturewhen in use, to the risk of the user.

It is a disadvantage of conventional electrode water heaters to have tocontend with the wide variation of water conductivity of drinking water,both in the United States and in other parts of the world. Waterconductivity is measured in microsiemens, which is the same as micromhos. Mhos are the inverse of ohms, and therefore represent theconductive characteristics of water, which absorbs more power as itbecomes more conductive. Water conductivity in the United States canrange from 50 microseimens to over 1,500 microsiemens. Foreign countriescan have as high as 1,800 microsiemens.

The disadvantage occurs when their electrodes must be sized such thatthey are capable of attaining satisfactory performance with 50microsiemen water, but must then regulate a potentially hazardous 30times the current draw when the water is at 1,500 microsiemens. Forexample, an electrode water heater on a 50-amp breaker must attain anacceptable performance of 40 degrees of temperature rise from its coldwater inlet to its hot water outlet. If the water is conductive to 50microsiemens and the heater passes 1 gallon per minute, the powerrequired is 26.8 amps at 220 VAC. In this case, there is no disadvantageto using an electrode since this is below the current rating of its50-amp breaker. If, for example the water conductivity is 1,500microsiemens, the potential load would then become 804 amps. This powermust be regulated to below the 50-amp circuit breaker and morespecifically, to the 26.8 amps to meet the 40-degree temperature rise at1 gallon per minute. The condition is exacerbated when 3 gallons perminute are required. The potential current draw for the flow rate is astaggering 2,400 amps.

Since prior to this invention, electrodes could not be resized on thefly, regulating this amount of power has been costly. Typically, thecommon approach to electrode water heaters design is to use triacs,IGBT's, mosfets and other sine wave chopping devices to regulate thehigh current so that the circuit breakers do not trip. For low powerrequirements such as light dimmers, this is the preferred andinexpensive method. However, to regulate the high current potentials ofelectrode water heaters, these methods are economically and technicallyunacceptable.

It is yet another disadvantage of electrode water heaters that suggestmethods of power regulation using said wave-chopping devices, that suchdevices can introduce harmonics in the line and heat the wiring withouttripping the circuit breaker. Wires can become extremely hot, causingserious fire hazard. One solution to this disadvantageous condition iscalled “current matching”. However, current matching for electrode waterheaters and boilers is nearly impossible to accomplish with such awidely varying electrical load without mechanically moving theelectrodes as is done in large, expensive industrial electrode boilers.To do this in a home appliance such as an instant water heater would betoo costly and would introduce wear parts that would greatly increasethe failure modes of the device.

Yet another disadvantage of electronically regulating high current viaAC wave chopping is the electromagnetic emissions that disruptcommunications television signals and create radio static interference.These emissions are not allowed in Europe's “Flicker Standard” and canviolate FCC regulations.

It is another disadvantage of electrode water heaters that in order tomatch the load to the line without the said expensive sine wave choppingdevices, the preferred method is to physically move the electrodes viaelectric motors. This is done to either increase their relative distancefrom each other, or to pull them upward leaving less of the electrodesubmersed, hence reducing their surface area disposed in water.

It is an object of this invention to provide an electrode water heaterwhose current draw is passively and automatically regulated withoutchopping the sinusoidal AC electrical power which heretofore wasnecessary to regulate 1,500 amps, or more, down to within the requiredamperages of household circuit breakers.

It is another object of this invention to provide this regulation withno moving parts.

It is yet another object of this invention to accomplish this regulationwith no electronic components such as triacs, IGBT's or mosfets sized toaccommodate the high currents mentioned.

It is another object of the invention to regulate water temperature toan acceptable temperature by utilizing the merits of a PositiveTemperature Coefficient conductive material that becomes non-conductiveat a known temperature, and where necessary, utilizing less expensivestate of the art electronic technology for a finer temperature setting.

It is another objective of this invention to regulate water temperatureby way of the water transferring its heat into the Positive TemperatureCoefficient material, and rendering it, or some varying portion thereofnon-conductive.

It is yet another objective of the invention to regulate a high inrushof current by way of the material's electrical resistance heating itselffrom within so that it, or some varying portion thereof becomesnon-conductive so as to appropriately reduce the active area of theiropposed conductive faces.

It is yet another object of the invention to utilize a dynamic phasechange location as a means to appropriately adjust the virtual effectivesize of the electrodes, in essence interpreting that dynamic as anelectrode that passively and automatically changes its size toaccommodate proper current draw and water temperature based on waterconductivity and/or water flow.

It is another object of the invention to provide a temperature controlvalve disposed between the inlet and the outlet of the water heater'shousing so as to provide a means to lower the outlet temperature of thewater to below the PTC temperature of the material.

It is yet another object of the invention to restrict the flow of waterthrough the water heater to a rate that will always allow for the PTCeffect to render the electrodes non-conductive.

It is another object of this invention to regulate potentially thousandsof amps with no electronic components. While the invention at firstappears to defy the laws of physics by regulating its potential amperagedraw without increasing its heat proportionally, as in the case ofvariable transformers, it must be understood that it is the load that ismodulating itself. The result is a kinetic servo loop. The inverseoccurs when the water's conductivity decreases, and an additionaldynamic occurs when the flow of water acts upon the electrode'stemperature the complex dynamics of which will become apparent in thedetailed description of the invention.

Any plastic electrode that can be used in a domestic water supply andthat exhibits PTC characteristics at an appropriate temperature todeliver usefully hot water can be used. However, other properties becomedominant when using them in affordable water heaters with a suitablylong life and a minimum usage of electrical current. Interestingly, itis not possible to boil water when plastic electrodes are used becausewhen boiling temperatures are reached, cavitation occurs on the surfaceand prevents the flow of electrical current. This saves the large costof temperature and pressure valves for standard water heaters.

For example, many plastic electrodes too quickly become coated withinsoluble mineral deposits, such as the carbonates of calcium andmagnesium, and other deposits which coat the electrode and limit itsuseful life. Purity of its ingredients is a prime requirement.

Other complications are the conductive transmissibility of electricalcurrent from the surface the electrode into the water on its surface.There is a puzzling relationship between the conductivity of theelectrode body itself and the connectivity of the surface in the water.

Still another complication is the need to reduce electrical consumptionin the electrodes itself. It should be remembered that the heating ofthe water itself, and not by thermal circuitry of the cool water withthe surface of the electrode. Embedded with these is the means tomanufacture the product. A conductive package to improve the grossfunctions can, if too much is needed, prevent the economical usage ofinjection molding. This invention solves this issue.

This invention proposes to solve in large part the above problems,thereby to provide an improved instant water heater.

BRIEF DESCRIPTION OF THE INVENTION

An instant water heater according to this invention comprises a heatingchamber having an inlet and an outlet. Water to be heated enters thechamber through the inlet, and after being heated, exits through theoutlet to a point of use.

A pair of spaced-apart Positive Temperature Coefficient electrodes ismounted in the chamber, so disposed and arranged that an appropriatevolume of the water passes between them so as to be heated by currentthat flows through the water from one electrode to the other.

According to a preferred application of the invention, the precisetemperature to which the water is heated is maintained by the additionof an electronic temperature control circuit. A first order temperatureis attained by the positive temperature coefficient conductive polymer'sphase change temperature and a more precise electronic temperaturesetting by the user. For this specific application of the invention, thePositive Temperature Coefficient electrodes have a phase changetemperature tolerance of several degrees F., and therefore are notnormally used for laboratory use for fine adjustment of temperature.Their purpose is to regulate the water temperature, to an acceptablefirst order temperature, and regulate current draw in amps. Apotentiometer dial setting can be adjusted to the desired finetemperature to within less than one degree F., or finer.

In most applications the order of magnitude to which the PTC electrodescan control temperature will be acceptable, thereby negating the needfor any electronic controls.

According to this invention the Positive Temperature Coefficientelectrodes are principally formed of, and their exposed surfaces arespecifically made of, either an electrically conductive ceramic orpolymeric resin.

According to a preferred but optional feature of the invention, thepolymer electrode is loaded with a “conductive package” comprising twoor more of the following: graphite as natural graphite, syntheticgraphite, purified graphite, expandable graphite, expanded graphite,graphite flake and graphite fiber, and carbon as carbon black, purifiedcarbon, carbon fiber, carbon fibrils, and carbon nano tubes to reducethe bulk electrical resistance of the material, provide suitableconductivity for the electrode, and to provide for enhanced connectivitywith the water. This conductive package is preferably provided in theform of a good packing ratio of assorted sizes and correct proportionsto give the best result as will later be described.

The Positive Temperature Coefficient (PTC) of the polymer relates to thetemperature at which the material makes a phase change from electricallyconductive to non-electrically conductive. The material maintains itscrystalline structure up to its PTC temperature, in most cases around 60degrees C., wherein it changes to an amorphous condition. Thistemperature is just short of the polymer's melt/flow point, but lowenough where the material maintains enough of its structural integrityfor the purposes of this invention.

When the polymer is below its phase change temperature, conductive pathsare inherently created to form conductive pathways through thecarbonaceous material. As the phase change temperature is approached,these paths disconnect. Since this is the point at which no additionalelectrical current can pass through the material, it ceases to increasein temperature and holds a “tripped” temperature while a maintainingtrickle current passes through it. Upon cooling, it returns to itsprevious crystalline structure whereby the components of the carbonpackage reconnect at least in part, but never in the exact sameformation as before. Not reconnecting in the exact way makes thematerial become more resistive the second time it is brought to itsphase change temperature. It continues to become more resistive forabout 3 or 4 more cycles where it then stabilizes to a resistance thatwill endure thousands, perhaps hundreds of thousands of cycles.

Since the PTC temperature of the polymeric or ceramic material istypically higher than a normally desired water temperature, say for ashower or washing hands, a water temperature control channel can bemolded into the main housing of the water heater, disposed between andconnecting the cold water inlet to the hot water outlet. This allows forcold water to bypass the heating chamber and mix directly with theexiting hot water. Perpendicular to this molded channel is a threadedneedle valve used for controlling the amount of cool water to be mixedinto the hot stream.

The above and other features of this invention will be fully understoodfrom the following detailed description and the accompanying drawings,in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing the basic components of anelectrode water heater.

FIG. 2 is a schematic drawing showing an electrode water heater with itselectrodes reduced in size to accommodate highly conductive water.

FIG. 3 is a schematic drawing showing a method of reducing the area ofopposed faces of electrodes without reducing their size.

FIG. 4 is a schematic drawing showing greater spaced apart electrodes asan alternate method of accommodating high conductivity water withoutreducing their size.

FIG. 5 illustrates a microscopic view of carbon fibers contacting eachother within the microstructure of a polymeric Positive TemperatureCoefficient conductive polymer when it is below its phase changetemperature, fibers being an illustrative example.

FIG. 6 illustrates a microscopic view of carbon particles with gapsbetween them within the microstructure of positive temperaturecoefficient conductive polymer when it is above its phase changetemperature.

FIG. 7 is a schematic drawing showing a conductive portion, a phasechange point and a non-conductive portion of a positive temperaturecoefficient conductive polymer when in use as an electrode within aninstant water heater.

FIG. 8 is a schematic drawing showing that the phase change point of theelectrodes has shifted toward the outlet of the water heater during anincreased flow of water, a decrease of water conductivity, a lowering ofthe current draw via its electronic controls, or any combinationthereof.

FIG. 9 is a schematic drawing showing the phase change point of theelectrodes very close to the inlet of the water heater indicatingextremely high conductivity water, or very low water flow or combinationthereof.

FIG. 10 is a schematic drawing showing the positive temperaturecoefficient state, meaning its entire temperature is below its phasechange temperature.

FIG. 11 is a schematic drawing showing the positive temperaturecoefficient polymer electrode in a totally nonconductive state meaningits entire temperature is above its phase change temperature.

FIG. 12 is a schematic drawing of an instant water heater showing itselectrodes, an inlet and outlet thermistor and a control box showing atemperature setting dial and an amperage setting dial.

FIG. 13 is a perspective view illustrating the water heater with itscover shown in phantom lines.

FIG. 14 is a section view showing the waters flow path through theheater, from the inlet, through the inlet ground screen, through andbetween the blades of the electrodes, through the outlet groundingscreen and out its outlet.

FIG. 15 is a perspective section view which shows the upper and lowerelectrodes and spacer pieces that direct the water in a predeterminedcircuitous path between their blade.

FIG. 16 is a section view of the water heater's inlet and outletlocations in phantom while illustrating the needle valve that bleedscool inlet water over to the outlet port to achieve a desired loweroutlet water temperature.

FIG. 17 is a perspective view of an optional variation of the PTC waterheater with electronic printed circuit board, inlet and outletthermistors, said water heater being the type used in laboratories orany use where temperature requires critical temperature regulation.

DETAILED DESCRIPTION OF THE INVENTION

Although this invention contemplates a number of physical arrangementsfor effective heating and for regulation of electrical current so as notto induce undesirable harmonics that can overheat electrical-wiring, theprincipal advantages of this invention are derived from the use ofunique PTC electrodes which they all use.

A basic schematic of a prior art electrode water heater is shown in FIG.1 (Prior Art). Water 2 flows between two electrodes 1 and 3 while power7 is regulated by way of an electronic circuit 9 to provide apre-selected water temperature based on a combination of the water'selectrical conductivity and the area of the opposed faces 5 of saidelectrodes 1 and 3.

Should the water conductivity become extremely high, a solution shown inFIG. 2 (Prior Art) for stopping a overcurrent condition would be toshorten the electrodes thereby reducing the area of their said opposedfaces 5 such that it would better match the available power to thewater's conductivity. However, should the water's conductivity drop, itis impossible to put the material back. This illustration, althoughsimplistic, will be more appreciated as the PTC effect on this inventionis further understood.

Since it is not possible nor practical to dynamically change anelectrode's length, another scheme is suggested in FIG. 3 (Prior Art)involving moving one electrode 3 in relation to the other, therebyreducing the area of said opposed face 5 to a much smaller area. Anotheroption shown in FIG. 4 suggests separating electrodes 1 and 3 therebyreducing the amount of current deployed into the water.

As will later be described in further detail, Positive TemperatureCoefficient Polymers are loaded with distinctive carbon and graphiteparticulates ranging from carbon black, one of the most common, tocarbon fibrils one of the most recently invented forms of carbon. Inessence, the basic theory behind the PTC effect is that any crystallinepolymer will experience a PTC effect when it reaches its softeningtemperature. FIG. 5 shows conductive paths (sometimes called “strings”)15 formed by carbon particles that touch or connect to other strings 17that together form conductive pathways throughout the material.

As the material passes through its phase change temperature, saidstrings 15 shown in FIG. 6 disconnect as shown at 19, and the gapsdisallow electrical conductivity, therefore to increase the material'selectrical resistance. Certain mixes become completely non-conductive ata temperature that, to a certain degree, can be selectably establishedby its formation.

An improved and simplified scheme of the invention is shown in FIG. 7.In cases where close or critical temperatures are required, the currentwill be controlled with electronic circuitry 27. Typical proportional,integral and derivative (PID) math is employed for tight servo-loopcontrol using thermistors or other temperature sensing devices.

For domestic or commercial use of hot water, such electronic circuitry27 is not necessary when taking advantage of the PTC effect of theelectrodes of this invention to joule heat water. In these applications,water flows 2 between said electrodes 1 and 3 while power 7 is appliedto them. It is understood that in FIG. 7, this is a medium flow rate ofa common faucet. Although this can vary greatly from faucet to faucet,for illustrating the value of the PTC effect on the invention, we shallcall this flow rate 1 gallon per minute. As water 2 makes its waythrough the heater between said electrodes 1 and 3, its temperatureincreases because it is contained between and within a conductive pathlength 21 of said electrodes 1 and 3. Upon reaching the PTC temperatureof said electrodes 1 and 3, said water no longer continues to heat. Saidconductive path length 21 terminates at the location 25 of the phasechange temperature of said electrodes 1 and 3. The remainingnon-conductive path length of said electrodes 1 and 3 is heated by thealready hot water of said conductive path length 21 and also by someresidual current passing through said electrodes 1 and 3. These-twosources of heat energy maintain the remaining said non-conductive pathlength 23 of said electrodes 1 and 3 at or above its PTC temperature.Therefore, the remaining said non-conductive path length 23 of saidelectrodes 1 and 3 discontinues its joule heating of the water becauseit is no longer conductive.

As said water flow 2 doubles, using the illustrative value of 2 gallonsper minute, FIG. 8 shows that the said conductive path length of water21 increases in length in comparison to FIG. 7, moving away from thewater heater's inlet and toward its outlet. The said PTC phase change 25location remains at the same temperature as in FIG. 7, but has movedbecause the flow has increased and has cooled the said conductive pathlength of water 21 in a proportional manner. Since the said water flow 2has increased by 100%, it takes 100% more energy to elevate the watertemperature to the PTC temperature. Therefore, said conductive pathlength 21 of said conductive electrodes 1 and 3 has doubled. However,the water output temperature remains the same, essentially theelectrode's PTC temperature.

As water flow is halved, using the illustrative value of ½ gallon perminute, FIG. 9 shows that the said conductive path length 21 decreasesin length in comparison to FIG. 7, moving toward the water heater'sinlet and away from its outlet. The said PTC phase change 25 locationremains again at the same temperature as in FIG. 7, but has movedbecause the flow has now decreased and the said conductive path lengthof water 21 has heated in a proportional manner. Again, but conversely,since the flow has decreased by 50% it takes 50% less energy to elevatethe water temperature to the PTC temperature. Therefore, the saidconductive path length 21 of said conductive electrodes 1 and 3 has beenhalved and again, the output temperature remains the same, essentiallythe electrode's PTC temperature.

It will be observed that an identical but inverse result as describedfor water flow occurs with variation in water conductivity.

As water conductivity lowers by 50% using the illustrative value of 1gallon per minute, FIG. 8 shows that the said conductive path length ofwater 21 increases in length in comparison to FIG. 7, moving away fromthe water heater's inlet and toward its outlet. The said PTC phasechange 25 location remains at the same temperature as in FIG. 7, but hasmoved because the waters conductivity has decreased and the flowingwater has cooled the said conductive path length of water 21 in aproportional manner. Since the said water conductivity has decreased by50% it takes 100% more path length to elevate the water temperature tothe PTC temperature. Therefore, said conductive path length 21 of saidconductive electrodes 1,3 has doubled. However the water outputtemperature remains the same, essentially the electrode's PTCtemperature.

As water conductivity doubles, using the illustrative value of anunchanged 1 gallon per minute, FIG. 9 shows that the said conductivepath length 21 decreases in length in comparison to FIG. 7, movingtoward the water heater's inlet and away from its outlet. The said PTCphase change location 25 remains again at the same temperature as inFIG. 7, but has moved because the water's conductivity has now increasedand the said conductive path length of water 21 has heated in aproportional manner. Again, but conversely, since the water conductivityhas increased by 100% it takes 50% less path length to elevate the watertemperature to the PTC temperature. Therefore, the said conductive pathlength 21 of said conductive electrodes 1,3 has been halved and again,the output temperature remains the same, essentially the electrode's PTCtemperature.

Attending to the complex dynamics of water conductivity and flow forelectrode water heaters has been expensive and difficult for regulatingoutput temperature. This invention passively compensates for both ofthese critical aspects of electrode water heating.

Of course, there are limits to the dynamics of the invention. However,when said electrodes 1 and 3 are sized properly in relation thevariations in water conductivity that is available from United Statesand other water infrastructures, acceptable flow rates and availablepower, the benefits of the invention are far more favorable than theprior art. FIGS. 10 and 11, although similar in appearance, illustratethese limits and the safety inherent in the invention.

When water enters at a flow rate above what the available power canheat, the entire said flow path 21 of said electrodes 1,3 becomesconductive. This is because said water 2 cools the entire saidelectrodes 1,3 to below their PTC temperature. Conversely, in FIG. 11,the said non-conductive path length 23 entirely encompasses saidelectrodes 1,3 rendering them into a non-conductive condition when thewater is shut off, or the flow is so low that their temperature iselevated to their PTC temperature. In the case where the water is shutcompletely off, the amount of water remaining inside the water heater isso small in comparison to a standard 40 gallon storage water heater thatthe stand-by heat loss through the walls of the water heater becomesinsignificant.

FIG. 12 is a schematic view of a PTC electrode water heater with addedcomponents and electronics used to maintain accurate outputtemperatures. Water 2 flows past an inlet thermistor 29, between saidelectrodes 1 and 3, is heated and its temperature measured by an outletthermistor 31. The electronics illustrated as item 27 of FIG. 12 can bedesigned and adapted by any competent electronics engineer. There aretwo user controls 35 and 33 that are unique to the invention and arenoteworthy. These consist of a current limit knob 35 that is used tolimit the amount of current that can be drawn by the water heater and anoutlet water temperature knob 33 used to set the temperature of thewater.

In FIG. 13, an instant PTC water heater 15 is shown in perspective viewwith its plastic injection molded cover 41 removed and outlined inphantom. A main housing 47, a bottom cover 57 and an inlet/outletmanifold 55 comprise the major components of the instant PTC waterheater. Water enters 49 at the inlet side of said manifold 55 and exits51 at the outlet side of manifold 55.

An electrical cord 53 is secured to its three respective lugs, namelythe power lugs 39,40, and a grounding lug 40. A wire 61 is run from saidgrounding lug 38 to said manifold 55 and attached with a screw 59. Twowires run from said power lugs 30,40 to the electrode connections 45. Anangle bracket 56 is disposed on the top face of said bottom cover 57 andstaked in place via protruding molded-in studs. A throttle screw 44 isthreaded into a retaining plate 46 with matching threads. Turning saidknob 44 allows an adjustment for cool inlet water to mix with the hotwater thereby adjusting the outlet water temperature. The details ofwhich are shown in greater detail in FIG. 16.

FIG. 14 constitutes a section view of the embodiment of FIG. 13 thatshows heating of the water. The water inlet flow 49 entering said inletmanifold 55 and passing through a conductive plastic inlet screen 58through a molded-in channel 72 in said main housing 47 and between thetwo electrodes 65,67. The water takes a circuitous route between saidelectrodes 65,67 during which it is joule heated by electrical currentpassing through it. It exits through a molded-in channel 74 of said mainhousing 47 and past a restriction orifice 54. Restriction orifice 54 issized so that its flow rate limits the amount of water passing throughthe water heater. Limiting the flow insures that the performance of thewater heater meets a specific rated temperature rise. It also insuresthat higher flow rates do not cool the electrodes while passingpotentially high conductivity water that may draw excessive current. Thesaid restriction orifice 54 limits the flow so that the PTC effect ofsaid electrodes 65,67 will reach non-conductivity before exceeding theline's circuit breaker rating.

FIG. 15 shows a cut-away of the corner of the embodiment of FIG. 13illustrating said main housing 47, and said electrodes 65, 67. The watermaintains a circuitous path between the blades of electrodes 65,67 anddoes not spill over or under said blades, plastic spacers 73,76 aredisposed between said electrodes 65,67. These plastic spacers 73,76forcibly route the water only in the spaces 75 between the blades ofsaid electrodes 65,67. This long linear path length facilitates thecreation of a clear and concise place as shown in FIG. 7 at which saidPTC effect 25 is located within the total water path length.

FIG. 16 is a section view of a more refined embodiment of FIG. 13. Itshows said throttling screw 44 threaded into said retaining plate 46.Retaining plate 46 is fastened to main housing 47 with screws 80 andwashers 82. A seal retaining cup 78 is disposed between retaining plate46 and main housing 47 to compress resilient seal 85 against a smoothportion of throttling screw 44 so as to seal against leakage. Throttlingscrew 44 adjusts the water temperature to a desired temperature byincreasing or decreasing the space 91 between its end and the surface ofbottom housing 57. In operation, water enters molded-in channel 72through inlet orifice 89, whereby most of the flow 97 is directedbetween said electrodes. An adjustable percentage flows past saidthrottling screw 44 through opening 91 and mixes with exiting hot water95 leaving the water heater through exit orifice 93 at the desired watertemperature.

The object of this invention is not to define the operation ofelectronics required to regulate a PTC plastic electrode water heater,but to include the optional embodiment of controlling temperature moreaccurately through the use of electronics. FIG. 17 is an alternateembodiment of FIG. 13 showing a printed circuit board 101. Printedcircuit board with its electronics 101 serve to regulate the temperatureof the water in use to within smaller temperature tolerances. Such anembodiment requires that it incorporate a pressure sensing device 105that when in operation senses a pressure drop which activates saidelectronics. A current sensing device 103 provides input to amicroprocessor 107 that triggers the proper firing angle of the AC sinewave by way of triac 113 that is heat-sink mounted to a face 119 of theinlet/outlet manifold 121. An inlet thermistor 117 provides input to themicroprocessor when the flow of water stops by its increase intemperature. An outlet thermistor 115 provides input to themicroprocessor by measurement of the output temperature of the water.

The preferred conductive package of this invention uses-carbon in two ormore of its forms. As previously mentioned, these carbonaceous materialsare physical forms of graphite and of carbon in various shapes. Physicalshapes make a considerable difference in this invention because muchdepends on linkage between adjacent particles, and conductance throughthem. Graphite flake offers advantages because of its shape andcross-section, for example.

The designer of these electrodes will consider their properties andtheir interlinking and separation in the two states of the plastic aboveand below the transition temperature.

It is a considerable advantage to proportion the sizes of the particlesused to provide an optimum “fit”. If only large particles were used,there would be considerable voids between them that would moreadvantageously contain conductive particles. Just as a pile of roundmarbles leaves voids between them which could be filled with smallparticles such as pebbles or sand, so with this invention smallerparticles, or even carbon black could be incorporated to advantage. Thisis called a “packing ratio” which relates to placing smaller particlesin voids between the larger ones. It is an attainable objective toprovide nearly identical electrical results with less loading of packedmaterial, thereby facilitating the manufacturer of the product byaffordable injection molding.

There are limitless combinations of these materials, from which thedesigner will select the one most appropriate to his intendedapplication. Graphite flake with interposed smaller graphite fibers andperhaps some carbon black constitutes one useful combination.

The amount of carbonaceous material to be added to the plastic materialis ordinarily determined by considerations of bulk resistivity (which islowered by the carbonaceous material) and the surface connectivity withthe water or other liquid to be heated (which increases with increasedcarbon). This is a “balancing act” which requires only some reasonabletrial and error work to establish an intended result. It is well withinthe skill of a good formulator.

It is important that the material used in these electrodes be as pure aspossible because of the tendency for salts to deposit on the electrodein a very short period of time if certain elements are in the materialswhere they act as “seeds” for deposition of insoluble salts. It isespecially important to eliminate the following: ions of calcium, iron,aluminum and silicon, and silicates and carbonates, especially calciumcarbonate. Unfortunately some of these elements get into the plasticmaterial during the manufacture of the plastic itself, and during themanufacture of the electrode, unless great care and preparation aretaken. Even medical grades of these plastics generally include enough ofthem to adversely affect the useful life of the electrode.

It is possible, with great effort, to produce plastic with sufficientlylow levels of impurity, and this is an unusual requirement for anoptimum electrode to be made. Similarly as to the carbonaceousmaterials. Carbonaceous materials are available in a purified condition,and these should be used.

In any event, the materials and their combination in the electrodeshould be as devoid of the aforementioned impurities as possible to theextent that the electrodes will have a significant life span. Foroptimum life span, impurities of the type described should be present inthe electrode in less than about 100 parts per million. It is possibleand preferred to keep them as close to 10 PPM as possible. Thecarbonaceous materials are available with almost no impurities. Themanufacturer/molder should be cautioned that surface contamination of apreviously used machine must be eliminated, lest these impurities enterthe product.

An important advantage of the packing ratio is that it provides betterconductivity with the use of less conductive packaging material. Thisenables better performance with less added material. As a consequencethe electrode material can more readily be injection molded. When toomuch conductive package must be added, injection moldability becomesquestionable because of the greatly increased pressures required by themachinery. Use of the injection molding process is highly advantageousbecause of it obvious economy. The use of this packing ratioconsideration reducing the amount of conductive material for the sameresults.

This invention is not to be limited by the embodiments shown in thedrawings and described in the description, which are given by way ofexample and not of limitation, but only in accordance with the scope ofthe appended claims.

1. An electrode for an instant water heater, said electrode beingintended for submersion in water to be joule heated for conductingelectricity for heating water disposed and in contact between itself anda confronting similar electrode, said electrode comprising: a polymerwhich at a lower temperature is conductive of electricity, and whichinherently has a positive temperature coefficient, whereby saidelectrode loses at least some of its electrical conductivity and becomesnon-conductive or nearly non-conductive at and above a temperature atwhich said polymer undergoes a phase change from crystalline toamorphous, whereby to reduce or substantially prevent passage ofelectrical current through it at and above said phase changetemperature, thereby to prevent heating of water in which it issubmerged to a higher temperature, and to remain in said crystallinephase at lower temperatures, and a conductive package of carbonaceousmaterial distributed throughout said polymer to provide enhancedelectrical conductivity at temperatures below said phase changetemperature and less enhanced at temperatures above said temperature,said conductive package comprising carbonaceous material in a pluralityof particle sizes, whereby more intimately to pack the carbonaceousmaterial into the polymer to facilitate molding of the electrode byinjection molding.
 2. An electrode according to claim w in which saidpolymer and carbonaceous material are being substantially devoid ofcontaminant material so that the concentration of contaminant in theelectrode is sufficiently low that seeds of insoluble salts formed fromthe water are unlikely to be formed on the surface of the electrode. 3.An electrode according to claim 1 in which said carbonaceous materialcomprises two or more of the following: natural graphite, syntheticgraphite, purified graphite, expandable graphite, expanded graphite,graphite flake and graphite fiber, and carbon as carbon black, purifiedcarbon, carbon fiber, carbon fibrils, and carbon nano tuber, thereby toreduce the bulk electrical resistance of the electrode, provide suitableconductivity for the electrode, and to provide for enhanced connectivitywith the water.
 4. An electrode for an instant water heater, saidelectrode being intended for submersion in water to be joule heated forconducting electricity for heating water disposed and in contact betweenitself and a confronting similar electrode, said electrode comprising: apolymer which at a lower temperature is conductive of electricity, andwhich inherently has a positive temperature coefficient, whereby saidelectrode loses at least some of its electrical conductivity and becomesnon-conductive to nearly non-conductive at and above a temperature atwhich said polymer undergoes a phase change from crystalline toamorphous, whereby to reduce or substantially prevent passage ofelectrical current through it at and above said phase changetemperature, thereby to prevent heating of water in which it issubmerged to a higher temperature, and to remain in said crystallinephase at lower temperatures; a conductive package of particles ofcarbonaceous material distributed throughout said polymer to provideenhanced electrical conductivity at temperatures below said phase changetemperature and less enhanced at temperatures above said temperature;said polymer and said carbonaceous material being substantially devoidof contaminant material so that the concentration of contaminant in theelectrode is sufficiently low that seeds of insoluble salts formed fromthe water are unlikely to be formed on the surface of the electrode. 5.An electrode according to claim 2 in which contaminant material iscontained in said electrode in total amount no greater than about 100parts per million of the electrode.
 6. An electrode according to claim 5in which said contaminant material is contained in said electrodes intotal amount no greater than between about 10 ppm and 100 ppm.
 7. Anelectrode according to claim 4 in which contaminants to be excluded areamong the following: ions of calcium, iron, aluminum and silicone, andsilicates and carbonates, especially calcium carbonates.
 8. Incombination: a pair of electrodes according to claim 4, spaced apartfrom one another in a chamber adapted to submerge them and apply anelectrical potential between them to heat the water by joule heating.